In general, rotating shafts installed in various drive power transmission mechanisms are rotatably supported by bearings. In this case, so-called ball bearings are often used. Ball bearings include a plurality of rolling elements (rolling members) arranged in a circumferential direction in a space between an inner ring and an outer ring. The rotational performance of rotating shafts can be increased by using bearings of this type.
This type of bearing is used as means for supporting a rotating shaft in a drive power transmission mechanism for various drive devices. Some drive devices are required to prevent foreign matter, such as dust and moisture, from intruding into an inner region thereof through a bearing section. If foreign matter intrudes into the bearing itself, there will be a problem that the rotational performance will be degraded or abnormal noise will be generated. To solve this problem, a seal member made of an elastic material may be arranged on the outer periphery of the rotating shaft in the vicinity of the bearing, so that the bearing section is waterproof and dustproof. However, in this case, the rotational performance of the rotating shaft is degraded due to the influence of a contact pressure applied by the sealing member made of an elastic material.
Bearings having magnetic fluid seal mechanisms in which magnetic fluid is used (hereinafter referred to as bearings with magnetic fluid seals) are known structures that prevent foreign matter from intruding into the bearing section without reducing the rotational performance of the rotating shaft. For example, PTL 1 discloses a ball bearing in which rolling elements are retained between an outer ring and an inner ring and in which a magnetic member is interposed between the outer ring and the inner ring that rotate relative to each other, the magnetic member being fixed at one side thereof and magnetic fluid being disposed in a seal gap provided at the other side of the magnetic member. More specifically, the magnetic member is disposed between the inner ring and the outer ring so as to block the rolling elements, the magnetic member being fixed at one side thereof and the magnetic fluid being disposed in the seal gap provided at the other side of the magnetic member. Accordingly, the rolling elements are tightly sealed and intrusion of foreign matter into a rolling element section, which affects the rotational performance, is prevented.